Fast retrain based on communication profiles for a digital modem

ABSTRACT

A digital modem for operating in a splitterless environment that supports fast retrain based on communication profiles. The modem includes a memory that stores a plurality of communication profiles, ADSL communication logic that sends and receives information via a phone line and that operates according to any one of the plurality of communication profiles, and signal quality monitor logic that continuously monitors communication on the phone line. The monitor logic provides a signal change indication if the signal quality changes by at least a predetermined amount. The modem further includes fast retrain logic that selects another one of the profiles stored in the memory in response to the signal change indication, that retrains the communication logic to operate according to the selected profile and that cooperates with the communication logic to transmit a fast retrain indication via the phone line to the central office ADSL modem. The digital modem may also include training or measurement logic that determines the communication characteristics of the phone line, that generates a corresponding profile and that sends the new profile to the other modem via the phone lines.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. applicationSer. No. 09/122,561 entitled “Virtual Gateway that Couples DifferentNetworks Over a Common Transmission Medium”, filed Jul. 24, 1998, whichis hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to digital modem that supports fastretrain based on communication profiles.

DESCRIPTION OF THE RELATED ART

Many personal computer systems (PC's) are sold with, or have the abilityto add, a communication device such as a digital or analog modem or thelike that enables communication with an external network via telephonewires from the home. The most common external network is the Internet,although other networks including broadband networks, public networksand wide area network (WANs) are contemplated. For simplicity, all suchexternal or broadband networks are referred to herein as WANs. Dial-upmodem technology is relatively easy to install and comfortable for theend user to use and currently operates up to a common data rate ofapproximately 56K bits per second (bps). The 56K bps dial-up modemsolution provides a significant increase in speed as compared to a 14.4Kbps modem, but does not provide a significant speed advantage ascompared to a 28.8K bps modem. The actual modem speed achieved isdirectly proportional to the quality of the channel characteristics ofthe voice band signal in a given home location. At the present time,none of the Internet Service Providers (ISP) are guaranteeing the actualrate for the end user.

One significant problem with analog modems are that they interfere withor otherwise cannot be used simultaneously with standard telephonesoperating according to the Plain Old Telephone Service (POTS) or MessageTelecommunications Services (MTS) and other voice band services. Thehome user is forced to install an entirely separate telephone line inorder to have simultaneous access to a WAN while maintaining standardtelephone service. An entirely separate and independent phone line isrelatively costly and inconvenient.

In spite of advances in dial-up technology, the explosive popularity ofthe Internet has caused consumers to become frustrated by the relativelyslow speed of their connection using analog modems. The IntegratedServices Digital Network (ISDN) service has been used at some home sitesand small businesses and offers somewhat higher speed access. However,access charges for ISDN are still high for the average consumer and itis not available everywhere. Also, each customer's loop must first bequalified in order to be connected. Digital Subscriber Loop (DSL)technology, particularly the asymmetrical DSL (ADSL), is beginning toemerge as the technology of choice to provide broadband access toconsumers. A digital class of modems supporting ADSL providessignificantly higher speed than either analog modems or ISDN devices.Furthermore, ADSL does not require a different type of transmissionmedia such as an ISDN line or the like. Traditionally, however, ADSLrequired a second phone wire to be installed within the home thatrequired a truck roll and possibly a POTS splitter to be installed atthe demarcation point at the home.

The LAN and broadband access issues are also applicable to the smalloffice environment. Small offices commonly include an entirely separatetelephone network, a separate LAN network and a separate WAN orbroadband connection through a separate physical medium connection suchas an ISDN line or the like.

One issue with using ADSL and POTS on the same transmission media isthat each phone handset changes the line quality and communicationcharacteristics of the transmission media, such as the characteristicimpedance, when on or off hook. Such change in the communicationcharacteristics of the transmission media effects ADSL operation, suchas the signal quality, divergence of equalizers, echo cancelers, carrierand timing recovery and other digital signal processing (DSP)algorithms, etc.

It is desired to use existing phone lines and to further providebroadband access without the requirement of a local POTS splitter orseparate phone lines. It is further desired to use standard telephoneservices on the same transmission medium such as a standard phone linewithout interfering with ADSL communications.

SUMMARY OF THE INVENTION

A digital modem that supports fast retrain based on communicationprofiles according to the present invention includes a memory thatstores a plurality of communication profiles. The modem also includescommunication logic that sends and receives information via atransmission medium and that operates according to any one of theplurality of communication profiles, and monitor logic that continuouslymonitors communication by the communication logic on the transmissionmedium according to any one of the plurality of communication profilesand that provides a signal change indication if the communicationcharacteristics change by at least a predetermined amount. The modemfurther includes fast retrain logic that selects another one of thecommunication profiles stored in the memory in response to the signalchange indication, that retrains the communication logic to operateaccording to the selected communication profile and that cooperates withthe communication logic to transmit a fast retrain indication via thetransmission medium.

In the embodiments illustrated, the digital modem is an ADSL modem thatoperates according to the Discrete MultiTone (DMT) modulation methodusing a plurality of upstream and downstream tones, where each tone iswithin one of a plurality of sub-channels or sub-frequencies of thetransmission medium bandwidth. The ADSL modem may operate at a homelocation without requiring a POTS splitter. The ADSL modem, otherwisereferred to as the Remote ADSL Termination Unit (ATU-R), communicateswith a Central Office ADSL Termination Unit (ATU-C) located at thecentral office of the telephone company. Because a POTS splitter is notpresent, the digital modem operates on the same phone lines ortransmission medium as one or more standard telephones operatingaccording to POTS. In this manner, POTS signaling and on/off hooktransitions of the telephones change the communication characteristicsof the phone lines and affect ADSL communications. The signal quality iscompromised so that the same data rate may not be maintained. However,communication may be continued at a lower data rate according to adifferent profile. The digital modem includes the fast retrain logic toautomatically switch between communication profiles to resumecommunications very quickly.

The digital modem may include measuring logic that cooperates with thecommunication logic to measure the communication characteristics of thetransmission medium and that generates and stores a correspondingcommunication profile in the memory. In at least one embodiment, each ofthe communication profiles are measured and stored in this manner. Uponinitialization of the modem, the measuring logic is employed to measurethe initial signal line quality, which typically reflects the optimalconditions of the phone lines while all of the telephones are on-hook.During operation, the monitoring logic detects a disturbance of thecommunications, such as when any one or more of the phones transition tooff-hook. If the communication profile is no longer valid where thecommunication logic is unable to sustain communications, and if the fastretrain logic determines that none of the profiles stored in the memoryare valid for the given status of the transmission medium, then themeasuring logic is again invoked to measure the communicationcharacteristics and generate a new communication profile. The newprofile is stored in the memory and sent to the other modem via thetransmission medium. Both modems retrain according to the newcommunication profile. Operation continues in this manner for any numberor up to a maximum number of profiles.

The monitoring logic also detects when a disturbance is removed and thecommunication characteristics improve. If so, the monitoring logicindicates to the fast retrain logic, which finds a better communicationprofile and quickly retrains the communication logic according to thebetter communication profile. Also, once all of the likely disturbancesare detected and measured and corresponding profiles are generated andstored, the fast retrain logic is able to quickly find the appropriateprofile and retrain the modem accordingly with little or no interruptionin communications.

In one embodiment, the digital modem measures the transmission mediumand stores only two different profiles including an initial best-caseprofile and a worst-case profile. If a new disturbance causes a greaterdepreciation of line quality than the current worst-case profile, then anew worst-case profile is generated which replaces the currentworst-case profile. The use of only two profiles simplifies the fastretrain indication. Upon receiving the fast retrain indication, bothmodems simply switch to the other stored profile. In the two profilebasic embodiment, the fast retrain indication may comprises a singletone generated on any one of the sub-channels. In the more complexembodiment in which a plurality of profiles are generated and stored,the fast retrain indication may comprise a plurality of tones thatidentify any one of the profiles. For example, the plurality of tonesmay implement a binary index to the plurality of communication profiles.In this manner, the remote modem is able to quickly determine theappropriate profile and retrain accordingly.

A modem system according to the present invention includes atransmission medium, a first digital modem implemented in a similarmanner described above, and a second digital modem that also includescommunication logic, fast retrain logic and memory for storing profiles.The second modem either receives the fast retrain indication andretrains its communication logic to operate according to the indicatedcommunication profile stored locally, or receives and stores a newcommunication profile and retrains its communication logic to operateaccording to the new communication profile. In an alternativeembodiment, the modems exchange the initial profile and independentlycalculate and store one or more other profiles based on the initialprofile and one or more predetermined cutback value. The predeterminedcutback values, for example, may comprise a certain signal-to-noise(SNR) reduction of one or more of the sub-channels.

A method of fast retraining first and second digital modemscommunicating across a transmission medium according to the presentinvention includes the first modem measuring the communicationcharacteristics under two different signal conditions of thetransmission medium, generating corresponding first and secondcommunication profiles and sending the first and second communicationprofiles to the second modem via the transmission medium. The methodfurther includes the first and second modems operating and communicatingvia the transmission medium according to either one of the first andsecond communication profiles. When the first modem detects a change ofthe communication characteristics of the transmission medium, it sends afast retrain indication to the second modem, and the first and secondmodems switch and operate according to the other communication profile.

The method may further include the first modem, after detecting a changeof the communication characteristics of the transmission medium,measuring the communication characteristics of the transmission mediumand generating a third communication profile.

The first modem then sends the third communication profile to the secondmodem via the transmission medium. The method may further include thefirst and second modems operating and communicating via the transmissionmedium according to any one of the first, second and third communicationprofiles. When the first modem detects a change of the communicationcharacteristics of the transmission medium, it selects another profileand sends a fast retrain indication to the second modem identifying theselected communication profile. The first and second modems then switchand operate according to the selected communication profile. The methodmay further include the first modem measuring the communicationcharacteristics under a plurality of different signal conditions of thetransmission medium and generating a corresponding plurality ofcommunication profiles. The first modem then sends the plurality ofcommunication profiles to the second modem via the transmission medium.The first and second modems operate and communicate via the transmissionmedium according to any one of the plurality of communication profiles.If the first modem detects a change of the communication characteristicsof the transmission medium, it selects a communication profile otherthan the current communication profile and sends a fast retrainindication to the second modem that identifies the selectedcommunication profile. Then, the first and second modems switch andoperate according to the selected communication profile. The fastretrain indication may comprise a plurality of tones to form an index tothe plurality of profiles.

It is now appreciated that a digital modem and modem system according tothe present invention enables efficient ADSL communications for a homelocation without a POTS splitter. Disturbances in the line or signalquality are detected and measured and a new profile is generated andexchanged between the modems. Both modems adapt to the new communicationcharacteristics by retraining according to the new communicationprofile. At least two profiles, including a best-case profile and aworst-case profile, enable communications to continue with little or nointerruption. When operating according to one of two profiles, if one ofthe modems detects a disturbance or removal of a disturbance, it sends afast retrain indication and both modems switch to operate according tothe other profile. A plurality of profiles may also be generated andused, where one modem determines the proper profile and asserts the fastretrain indication to identify the appropriate profile. In this manner,both modems quickly retrain according to the same profile and resumecommunications.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description of the preferred embodiment is consideredin conjunction with the following drawings, in which:

FIG. 1 is a block diagram of a network system including a virtualgateway system.

FIG. 2 is a block diagram of a network system similar to the networksystem of FIG. 1 except specifically using ADSL technology for the WANconnection.

FIG. 3 is a block diagram of another network system similar to thenetwork system of FIG. 1 except that the home location is replaced withtwo or more office locations for a small office environment.

FIG. 4 is a more detailed block diagram of one implementation of thegateway access node of FIG. 1.

FIG. 5 is a more detailed block diagram of another implementation of thegateway access node of FIG. 1.

FIG. 6 is a graph illustrating one method of separating operatingmethods of the LAN, WAN and telephone systems to enable simultaneouscommunications by separating frequency bands.

FIG. 7 is a block diagram of a network system including an ADSL digitalmodem system and method implemented according to the present invention.

FIG. 8 is a simplified block diagram of the ADSL modem of FIG. 7.

FIG. 9 is flowchart diagram illustrating a fast retrain method accordingto the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a network system 100 is shown including avirtual gateway system. A home location 104 is wired with a transmissionmedium 102, such as standard four wire twisted-pair telephone linescommonly used in homes throughout the United States. In the embodimentshown, the transmission medium 102 comprises telephone wires routed froma central office 106 of the telephone company (Telco) to the home site104 establishing an unbroken metallic path. Other transmission media arecontemplated, such as coaxial cables, various types of twisted-pair wireconfigurations, fiber optic cables, etc. and may also include one ormore wireless connections as desired.

The transmission medium 102 enters the home location 104 via a standardnetwork interface device demarcation (D) 108 and then is routedthroughout the home location 104 in any manner as desired. A pluralityof phone line connectors 110 are provided, each for enabling extensionof the transmission medium 102 for connection to a network device via acompatible connector. For example, the transmission medium 102 may berouted to standard RJ-11 telephone plugs installed throughout the homelocation 104 to connect computers and telephones using correspondingRJ-11 plugs. Each connector 110 refers to the plug, the jack or both.

A gateway access node 112 is coupled to the transmission medium 102 viaa single connector 110. The transmission medium 102 is coupled to alocal area network interface (LAN I/F) 114 within the gateway accessnode 112, where the LAN I/F 114 further interfaces to gateway logic 116.Likewise, a wide area network interface (WAN I/F) 118 within the gatewayaccess node 112 is coupled to the transmission medium 102 via the sameconnector 110, where the WAN I/F 118 further interfaces to the gatewaylogic 116. The LAN and WAN I/Fs 114, 118 each primarily include theappropriate hardware and hardware interfaces, such as PHY devices or thelike and expansion or peripheral buses etc., for establishing acommunication link between the transmission medium 102 and the processorof the gateway access node 112. The gateway logic 116 includesappropriate software components, such as one or more LAN and WAN devicedrivers, and gateway software for establishing a communication linkbetween the LAN and WAN drivers. The gateway logic 116 also comprisesappropriate hardware portions, such as the memory and processing devicesfor executing the software portions.

One or more computer systems or PCs, each implementing a local networknode 120, are also coupled to the transmission 102 via correspondingconnectors 110 in a similar manner as described for gateway access node112. Each node 120 includes a LAN I/F 122 that couples to thetransmission medium 102, where the LAN I/F 122 further interfaces to LANlogic 124 within each node 120. Each LAN I/F 122 includes theappropriate hardware components for establishing LAN communications viathe transmission medium 102 as known to those skilled in the art ofnetwork communications. The LAN logic 124 includes the appropriatesoftware, such as LAN software and drivers, and the appropriatehardware, such as memory and processing circuitry.

It is appreciated that the home location 104 may be “wired” using thetransmission medium 102 in any desired manner for coupling as manycomputers or nodes 120 to the gateway access node 112 via thetransmission medium 102 depending upon the particular LAN configurationlimitations. Various LAN configurations are contemplated, such asvariations of the standard 10BaseT or Fast 100BaseT Ethernet® solutions,FDDI, CDDI, ATM, etc. In this manner, a user at the home location 104may establish a LAN system including as many computer systems as desiredfor sharing files and various resources throughout the home location104.

The central office 106 is remotely located relative to the home location104 but coupled to the same transmission medium 102. The central office106 includes a POTS splitter 130 coupled to the transmission medium 102and a WAN I/F 132 coupled to the POTS splitter 130. In this manner, theWAN interface 118 of the home location 104 establishes a WANcommunication link with the WAN interface 132 at the central office 106via the transmission medium 102 on both sides of the demarcation 108.The WAN interface 132 at the central office 106 may further be coupledto an appropriate router 134 and an Internet Service Provider (ISP) 136to establish communications with the WAN 138, which comprises anyexternal network system, such as, for example, the Internet. In thismanner, the user at the home location 104 has access to the WAN 138 viathe gateway access node 112, the transmission medium 102 and the WANinterface 132 of the central office 106.

It is further noted that the gateway logic 116 is implemented to enablecommunications between the LAN I/F 114 and the WAN I/F 118. In thismanner, the LAN system established at the home location 104 includingthe nodes 120 and the gateway access node 112 has access to the WAN 138via the gateway access node 112 and the transmission medium 102. It isfurther noted that the LAN and WAN communications are simultaneouslyoperated on the same transmission medium 102 without having to install aPOTS splitter at the home location 104.

A plurality of standard telephones 140 are also coupled to thetransmission medium 102 at the home location 104 via correspondingconnectors 110. A POTS line card 142, such as a Subscriber LineInterface Circuit (SLIC) device or the like, is coupled to the POTSsplitter 130 at the central office 106 for establishing communicationswith the telephones 140 at the home location 104. The POTS line card 142of the central office 106 enables the user at the home location 104 toestablish telephonic communications using any one or more of thetelephones 140. It is further noted that the user may simultaneously useany telephone 140 to make a phone call without interruption of the LANsystem at the home location 104 and without interruption of the WANcommunication link between the home location 104 and the central office106. In this manner, at least two separate network systems are operatedsimultaneously with standard telephone services on the same transmissionmedium 102.

The gateway logic 116 transfers communication from the LAN to the WANlink and vice versa. For packet-based communications, such as Ethernet®or the like, the gateway logic 116, via the LAN I/F 114, retrievespackets from the transmission medium 102 on the LAN intended for the WAN138. The packets are converted and then transmitted onto thetransmission medium 102 via the WAN I/F 118 to the POTS splitter 130 ofthe central office 106. Response packets or any packets from the WAN 138intended for the LAN system of the home location 104 are routed to theWAN I/F 132 and the transmission medium 102. The WAN packets areretrieved from the transmission medium 102 by the gateway logic 116 andthe WAN I/F 118. If intended for any of the node 120 of the LAN system,the gateway logic 116 converts and transmits the packets onto thetransmission medium 102 via the LAN I/F 114 according to normal LANprotocol.

FIG. 2 is a block diagram of another network system 200, which issimilar to the network system 100 except that the WAN communication linkis established using ADSL technology. In particular, the WAN interface118 of the gateway access node 112 is replaced with a Remote ADSLTermination Unit (ATU-R) 204 and the WAN interface 132 at the centraloffice 106 is replaced with a Central office ADSL Termination Unit(ATU-C) 202. It is noted that various other DSL technologies (xDSL) arealso contemplated to establish the WAN communication link. Operation issimilar to the network system 100 where WAN communications are accordingto ADSL.

FIG. 3 is a block diagram of yet another network system 300, which issimilar to the network system 100 except that the home location 104 isreplaced with two or more office locations 304 and 306 to represent asmall office environment. The transmission medium 102 is providedthrough a standard demarcation 108 and is further split into two LANsegments for the office locations 304 and 306, respectively. A junction302 either comprises a direct physical connection between the LANsegments of the locations 304 and 306 or alternatively includes arepeater or switch for linking two or more LAN segments of thetransmission medium 102.

The first LAN segment of the office location 304 includes a gatewayaccess node 306, which is implemented in a similar manner as the gatewayaccess node 112 and which is coupled to the transmission medium 102 in asimilar manner via a connector 110. The office location 304 furtherincludes one more workstation nodes 308, each implemented in a similarmanner as the nodes 120 previously described and coupled usingcorresponding connectors 110. The office location 304 may furtherinclude one more telephones 140 coupled to the transmission medium 102using corresponding connectors 110. The office location 306 isconfigured in a similar manner and includes one or more workstationnodes 308 and one or more telephones 140 coupled to the transmissionmedium 102 using corresponding connectors 110. However, the officelocation 306 need not include another gateway access node 306.

The workstation nodes 308 of the office location 304 establish a firstLAN segment and the workstation nodes 308 within the office location 306establish a second LAN segment, where each LAN segment and thecorresponding workstation nodes 308 all effectively operate on the sametransmission medium 102 or extensions thereof. Furthermore, both LANsegments have access to WAN communications via the gateway access node306 over the same transmission medium 102. In a similar manner asdescribed previously, the gateway access node 306 establishes acommunication link with a WAN interface in a central office of atelephone company, such as the central office 106 described in FIG. 1.In this manner, a LAN may be further divided into several LAN segmentswhere each segment has access to WAN communications via a common gatewayaccess node 306 and transmission medium 102.

Referring now to FIG. 4, a block diagram is shown of one embodiment ofthe gateway access node 112. A connector plug 110 is shown for extendingthe transmission medium 102, which is further coupled to an interfacecircuit 401 for WAN communications and another interface circuit 405 forLAN communications. The interface circuit 401 is coupled to a WAN PHYdevice 402 and the interface circuit 405 is coupled to a LAN PHY 406.The WAN PHY 402 is further coupled to a WAN data pump 403, whichincludes any processing logic and buffer memory necessary fortransferring data between the WAN PHY 402 and a hardware interface 404of the gateway access node 112. The LAN PHY 406 is coupled to a LAN datapump 407, which includes any processing logic and buffer memorynecessary for transferring data between the LAN PHY 406 and the hardwareinterface 404. The interface circuit 401, the WAN PHY 402 and the WANdata pump 403 implements a WAN port for WAN communications, and theinterface circuit 405, the LAN PHY 406 and the LAN data pump 407implements a LAN port for LAN communications. The LAN and WAN ports maybe implemented on an expansion card 408 configured to plug into anappropriate socket or slot of the hardware interface 404. The expansioncard 408 and the hardware interface 404 collectively serve as theprimary hardware portion of a virtual gateway system.

The hardware interface 404 generally represents one or more buses and/orports and interfaces for enabling one or more external communicationlinks. For example, the hardware interface 404 may include one or moreexpansion or peripheral or other (I/O) buses, a video bus, a memory bus,an, etc. as is commonly found in computer systems. Also shown coupled tothe hardware interface 404 is system memory 412, which may furtherinclude volatile memory such as random access memory (RAM) or the likeand possibly non-volatile memory such as read only memory (ROM) or thelike. A central processing unit (CPU) or processor 414 is shown coupledto the hardware interface 404 for accessing and executing software,programs, device drivers, etc. loaded into the system memory 412. One ormore storage devices or drives 416 may be provided and coupled to thehardware interface 404, where the drive(s) may include one or morefloppy disk drives, hard disk drives, CD ROM drives, tape drives, etc.The hardware interface 404 is also shown interfaced to the gateway logic116, which represents the software portion of a virtual gateway system.The gateway logic 116 may be stored on the drive(s) 416, loaded into thesystem memory 412 and executed by the processor 414.

The gateway logic 116 includes a WAN driver stack 420 for controllingWAN communications, where the WAN driver stack 420 interfaces with theWAN port via the hardware interface 404. The gateway logic 116 alsoincludes a LAN driver stack 422 for interfacing with the LAN port viathe hardware interface 404. Gateway software 424 is provided forenabling a communication link between the driver stacks 420 and 422. Inparticular, information in the form of data or packets from the LANsystem may be transferred to the WAN communication link via the gatewaysoftware 424 of the gateway logic 116 and vice versa. The gatewaysoftware 424 generally interfaces an operating system 426 of the gatewayaccess node 112, which further interfaces one or more LAN and WANapplications 428.

In general, LAN communications over the transmission medium 102 for thegateway access node 112 are handled by the LAN PHY 406, the LAN datapump 407, the LAN driver stack 422, the operating system 426 and the LANportion of the applications 428.

WAN communications are handled by the WAN PHY 402, the WAN data pump403, the WAN driver stack 420, the operating system 426 and the WANportion of the applications 428. Information from the LAN system may betransferred to the WAN system by transmitting data from the LAN driverstack 422 to the WAN driver stack 420 via the gateway software 424.Likewise, WAN communications intended for the LAN system are transferredby transmitting data from the WAN driver stack 420 to the LAN driverstack 422 via the gateway software 424. In this manner, a local LANsystem has access to the WAN 138 via the gateway software 424, and thushas access to any desired broadband network such as the Internet.

Referring now to FIG. 5, a block diagram is shown of a gateway system500 illustrating another embodiment of the gateway access node 112 usingADSL technology. Again communications are handled via the connector 110and the transmission medium 102, which interfaces to a hardware portion502 of the gateway system 500. A solid line 504 generally represents aseparation between the hardware and software portions of the gatewaysystem 500. The hardware portion 502 includes a line I/F 506, whichincludes the circuitry to multiplex transmit and receive data betweenthe hardware portion 502 and the transmission medium 102. The line I/F506 is coupled to a LAN physical device (PHY) 508 and to an ADSL PHY510. The line I/F 506 transfers LAN data between the LAN PHY 508 and thetransmission medium 102 and transfers WAN data between the ADSL PHY 510and the transmission medium 102.

The hardware portion 502 interfaces with a set of drivers 512. Thedrivers 512 include a hardware I/O port driver layer 514 thatestablishes communication with both the LAN PHY 508 and the ADSL PHY510. The H/W driver layer 514 further interfaces a LAN device driver 516and an ADSL device driver 518. The LAN device driver 516 and the ADSLdevice driver 518 both interface with operating system drivers andinterface 520. In the embodiment shown, the operating system drivers andinterface 520 communicates with a WINDOWS® application interface layer524. A solid line 522 denotes separation between the operating systemand application layer of the gateway system 500. The WINDOWS®application interface layer 524 further interfaces a user LANapplication 526 and a user ADSL application 528.

In this manner, LAN communications are handled via the transmissionmedium 102 and line I/F 506 through the LAN PHY 508, the H/W driverlayer 514, the LAN device driver 516 and the user LAN application 526via the operating system drivers and interface 520 and the WINDOWS®application interface layer 524. WAN communications are handled via theADSL PHY 510, the H/W driver layer 514, the ADSL device driver 518 andthe user ADSL application 528 via the operating system drivers andinterface 520 and the WINDOWS® application interface layer 524.

A communication link 530 is also provided between the LAN device driver516 and the ADSL device driver 518. In this manner, LAN informationintended for transmission to the WAN 138 is transferred via the link 530from the LAN device driver 516 to the ADSL device driver 518. The ADSLdevice driver 518 converts and transmits the information to thetransmission medium 102 in WAN format via the ADSL PHY 510. Likewise,WAN information intended for the LAN system is converted by the ADSLdevice driver 518 and transferred to the LAN device driver 516 via thelink 530. The LAN device driver 516 transmits the information in LANformat to the transmission medium 102 via the LAN PHY 508. In thismanner, a virtual gateway is provided between the drivers 516 and 518.It is noted that gateway security, filtering and firewall functions maybe incorporated to prevent unauthorized communications between the LANand WAN. Such security, filtering and firewall functions are providedwithin the LAN device driver 516.

Several methods are available for determining whether information fromthe LAN system is intended for transmission on the WAN communicationlink and vice versa. In one embodiment using a packet-switchedcommunications, a particular field comprising one or more bits withineach LAN packet indicates whether the packet is destined to remainwithin the LAN system or is to be broadcast via the WAN communicationlink. A corresponding field in each WAN packet is used to identifypackets on the WAN communication link intended for the LAN system.Alternatively, a header or trailer may be appended to each packet thatincludes a destination identifier indicating whether the packet isintended for a LAN or WAN destination. Alternatively, the gateway accessnode 116 and the nodes 120 may each be assigned a separate IP address.The WAN 138 transmits packets using TCP/IP with the LAN system IPaddresses to the home location 104 via the ISP 136, the router 14 andthe central office 106. The gateway access node 116 receives anddistributes the packets based on the IP address. Of course, manydifferent techniques are possible and may depend upon the particular LANprotocol chosen by the user.

Referring now to FIG. 6, a graph is shown illustrating one way ofseparating operating methods of the LAN, WAN and telephone systems toenable simultaneous communications. In this case, the separation isachieved by using different frequency bands for each system. The powerspectral density (PSD) for each communication system is plotted versusfrequency in kilohertz (kHz). A frequency band 602 for standardtelephones operating according to POTS is located between 0 and 4 kHz.ADSL communications are provided in two separate intermediate frequencybands including an upstream portion 604 for transmitting informationfrom the home location 104 to the central office 106 via thetransmission medium 102 and a downstream portion 606 for transmittingdata in the opposite direction from the central office 106 to the homelocation 104. The upstream portion 604 of ADSL is located between astart frequency denoted “f1” and a stop frequency denoted “f2”. Thedownstream portion 606 of ADSL is located between a start frequencydenoted “f3” and a stop frequency denoted “f4”.

In one embodiment for ADSL, the start frequency f1 for the upstreamportion 604 is preferably 30 to 40 kHz and the stop frequency f2 isbetween 130 and 200 kHz. For the downstream portion 606, the startfrequency f3 is greater than 200 kHz such as 240 kHz and the stopfrequency f4 is between 390 kHz and 1.5 MHz.

The LAN communications are located in a higher frequency band 608 thanthe ADSL communications in the embodiment shown. In particular, the LANcommunications are provided between a start frequency “f5” and a stopfrequency “f6”. The frequencies f5 and f6 may be any practical frequencyabove 1.5 MHz to ensure no interference between the LAN and WANcommunications and to provide sufficient bandwidth for the data ratesdesired. For example, the start frequency f5 may be located at anyfrequency from 2 MHz or higher with a frequency range suitable for LANcommunications.

It is noted that alternative schemes are possible for ensuringindependence and non-interference between the LAN and WAN communicationprotocols. For example, the LAN and WAN frequency bands may overlap oreven be located in the same frequency band, where the LAN and WANinterfaces include appropriate circuitry and logic for multiplexing LANand WAN communications in time. A LAN/WAN multiplexing scheme, however,is more complex and requires a more sophisticated protocol scheme toensure proper operation and non-interference. The use of differentfrequency bands to separate the different network communications is asimpler and less complex solution.

Referring now to FIG. 7, an exemplary network system 700 is shown toillustrate a digital modem system and method that supports fast retrainbased on communication profiles according to the present invention. Thenetwork system 700 is similar to the network system 200 using ADSLtechnology, except that the home network or LAN configuration at a homelocation 702 is optional and not shown. The central office 106 includesthe POTS splitter 130 coupled to the transmission medium 102, andfurther includes the ATU-C 202 and the POTS line card 142 coupled to thePOTS splitter 130 as previously described. The home location 702includes several standard telephones 704, 706 and 708, each coupled tothe transmission medium 102 via corresponding connectors 110. The phones704, 706 and 708 each include a corresponding handset 705, 707 and 709,respectively. It is noted that one or more low pass filters (LPF) may becoupled between each phone 704, 706 and 708 and the transmission medium102 if desired. For example, an optional LPF is shown coupled betweenthe phone 708 and the transmission medium 102, which shields the phone708 from the ADSL communication frequencies and causes the phone 708 toact like a linear device by cutting off non-linear signals. An ADSLmodem 710 (ATU-R) is also coupled to the transmission medium 102 via aconnector 110 for enabling a WAN communication link for a computer 712.The ADSL modem 710 may be configured in any desired manner, such as anexternal modem or an internal modem that plugs into an expansion bus ofthe computer 712.

The ADSL modem 710 operates according to any DSL configuration using anytype of modulation method. Although a full rate ADSL system may be used,the present invention is illustrated using Universal ADSL (U-ADSL) basedon modifications to the current standard document Ti.413 Issue 2. Themodulation method illustrated is Discrete MultiTone (DMT) using 32upstream tones and 128 downstream tones as compared to 256 downstreamtones for full rate. In general, the frequency range of the transmissionmedium 104 is divided into a plurality of sub-channels orsub-frequencies, where each sub-channel is an independent channel withits own stream of signals. In order to enable communication, it isdesired to determine the signal-to-noise (SNR) ratio for eachsub-channel to determine the overall data rate of the channel. Theoverall data rate is the number of sub-channels times the number of bitsper sub-channel times the modulation rate, where the modulation rate is4KHz for each sub-channel. The number of bits per sub-channel dependsupon the SNR for that sub-channel.

The ADSL modem 710 operates according to Forward Error Correction (FEC),which is based on the Reed Solomon coding method. After power up andoptional self-test, the ADSL modem 710 participates in an activation andacknowledgment phase and transmits activate or tone requests to theATU-C 202. The ATU-C 202 responds with an activation signal oractivation tones. The ADSL modem 710 and the ATU-C 202 then determinethe relevant attributes of the transmission medium 102 using transceivertraining and analysis procedures. The ADSL modem 710 measures thecommunication characteristics of the transmission medium 102, such asthe characteristic impedance, the SNR for each sub-channel, the linequality, etc. and generates an initial profile of the channel ortransmission medium 102. The initial profile includes bits and gains(B&G) tables, FEC parameters R (redundant check bytes) and S (number ofsymbols per R-S codeword) values, the interleaver depth (D), and thepower spectral density (PSD) level.

FIG. 8 is a simplified block diagram of the ADSL modem 710. Thetelephone line r transmission medium 102 is coupled to Analog Front End(AFE) and Line Drivers circuitry 802 that converts digital transmit (TX)signals to analog for transmission and samples analog signals receivedand converts the analog signals to digital receive (RX) signals. The AFE& Line Drivers circuitry 802 also performs digital filtering. The RXsignals are provide to, and the TX signals are generated by, a DMTtransceiver 804. The DMT transceiver 804 includes decoding,descrambling, filtering, timing, synchronization and phase lock loop(PLL) circuitry as well as equalizers, digital signal processing (DSP)loops, echo cancelers, etc. The AFE & Line Drivers 802 and the DMTTransceiver 804 collectively comprise communication logic for the ADSLmodem 710 for receiving and transmitting data on the transmission medium102. Signal quality monitor logic 806 monitors DMT signals received bythe DMT transceiver 804, determines if the signal quality changes by atleast a predetermined amount and provides a signal quality changeindication. The signal quality may depreciate or improve depending uponwhether a disturbance is added or removed, respectively.

Measurement or initialization and training logic 810 cooperates with theDMT transceiver 804 to perform the initial communication characteristicmeasurement of the channel on the transmission medium 102 and togenerate the initial or best-case communication profile. The traininglogic 810 then stores the initial profile into a memory 812. Subsequentoperation of the training logic 810 depends upon the configuration andembodiment. In one embodiment, the training logic 810 is configured tocalculate and store at least one more communication profile into thememory 812. For a two profile configuration, the training logic 810calculates a worst-case profile based on the initial bestcase profile byusing a predetermined cutback value or decibel (dBm) drop. Inparticular, once the initial profile is measured and exchanged, thetraining logic calculates and stores in the memory 812 the worst-caseprofile using the predetermined cutback for each subchannel ofthefrequency band. Alternatively, the training logic 810 calculatesaplurality of communication profiles as described below for storage inthe memory 812.

In measurement embodiments, the training logic 810 cooperates with theDMT transceiver 804 to measure at least one more communication profile,and then stores each profile into the memory 812. If the signal qualitymonitor logic 806 determines that the signal quality has changed or thatthe SNR has dropped by a significant degree or a predetermined amount,and if the memory 812 does not include a stored profile that enablescommunication, then the training logic 810 is employed to initiatemeasurement of the transmission medium 102 and generation of acorresponding communication profile.

In general, the equalizers in the DMT transceiver 804 and the signalquality monitor logic 806 continuously monitor the SNR for eachsub-channel during operation by taking the difference between the actualor received symbol received on a sub-channel and the theoretically idealsymbol. If a disturbance on the transmission medium 102 causes asignificant drop of signal quality or SNR for any one or moresub-channels so that the current profile is no longer valid, the signalquality monitor logic 806 provides a signal quality change indication tofast retrain logic 808. A memory 812 stores one or more communicationprofiles P1, P2, P3, etc. for selection by the fast retrain logic 808.The profiles stored in the memory 812 preferably includes at least theinitial profile and at least one calculated or measured “worst-case”profile as further described below. If the fast retrain logic 808determines that at least one existing profile within the memory 812 issufficient to maintain communications, then the fast retrain logic 808selects a known profile and reprograms or retrains the DMT transceiver804 according to the new profile. Such training involves re-adapting theequalizers and DSP loops to the new (and usually reduced) data rate.Operation is able to continue without significant interruption, althoughat a reduced data rate depending upon the selected profile. It has beendetermined that fast retrain may occur on the order of severalmilliseconds (ms) to one or two seconds, which is significantly lessthan a full retrain procedure potentially lasting several seconds.

If, however, the fast retrain logic 808 determines that none of theexisting profiles within the memory 812 is sufficient to maintaincommunications, then the fast retrain logic 808 provides a new profileindication to the training logic 810, which initiates anothermeasurement of the channel on the transmission medium 102 to performanother full retrain procedure. A new communication profile is generatedand stored in the memory 812. The new communication profile is thenselected and the DMT transceiver 804 is retrained accordingly.

The initial profile is preferably measured during the best communicationconditions of the transmission medium 102 at the home location 702, sothat the initial profile is preferably the “best-case” profile. Forexample, to achieve the best-case profile, it is desired that no othercommunications are occurring during initialization, and that thehandsets 705, 707 and 709 of the respective phones 704, 706 and 708 areon-hook. For purposes of illustration, the handsets 705 and 707 areshown on-hook, while the handset 709 is shown off-hook. Each phone has adifferent impedance between on-hook and off-hook that affects thefrequency band of the transmission medium 102 and generally changes theSNR for one or more of the sub-channels used for communication betweenthe ADSL modem 710 and the ATU-C 202. An off-hook phone generallyreduces the signal quality and the SNR of one or more sub-channels.

A reduction of SNR for any one or more sub-channels results in acorresponding reduction in the performance of, and data rate achievableacross, the transmission medium 102. The signal processing routines ofeither or both of the modems ATU-C 202 and the ADSL modem 710 train upto the channel (carried on the transmission medium 102) and determinethe best data rate based on the given channel noise. The data rate isdetermined by measuring the maximum bit rate and gain for eachsub-channel under the current noise conditions of the channel, resultingin a B&G table which comprises the primary portion of the correspondingcommunication profile. After the initial profile is determined, the ADSLmodem 710 transmits the initial profile to the ATU-C 202 during anexchange phase. The ATU-C 202 and the ADSL modem 710 each program theirrespective transceivers according to the initial profile. In thismanner, the transceivers of the respective ATU-C 202 and the ADSL modem710 are matched to produce and appropriately respond to a specific setof precisely-timed signals on the transmission medium 102.

After full initialization, the signal quality monitor logic 806 of theADSL modem 710 continuously monitors the signal quality and SNR of eachtone during communication with the ATU-C 202 across the transmissionmedium 102. Disturbances occur on the transmission medium 102 due toringing of the phones 704, 706 and 708, in-premises noise pick-up andon/off hook transitions of the phones. Some disturbances, such asvarious kinds of in-premises noise pick-up cause only a relativelyinsignificant reduction of SNR so that communication may be continuedusing the same communication profile. However, other disturbances, suchas POTS signaling and handset on/off hook transitions, significantlydegrade signal and line quality. Such disturbances may effectivelyterminate ADSL communications on the transmission medium 102, so that anew profile must be used.

In a fast retrain method according to the pre-calculated embodiment, aworst-case profile is calculated using the initial profile and apredetermined cutback value or dBm drop. In particular, once the initialprofile is measured and exchanged, the ADSL modem 710 and the ATU-C 202each independently calculate and store the worst-case profile using thepredetermined cutback for each sub-channel of the frequency band. Inthis manner, a new B&G table is calculated within each modem. It isnoted that the R and S values, the interleaver depth D, and the PSDlevel need not be re-calculated and the initial measured values may beused for all other profiles. Thus, these values need not be exchangedagain between the ADSL modem 710 and the ATU-C 202. In FIG. 8, forexample, the profile P1 may be the initial or best-case profile whereasP2 is the worst-case profile. During operation, the ADSL modem 710detects a disturbance, determines that the initial profile may no longerbe used, switches to the worst-case communication profile and sends aswitch or fast retrain indication to the ATU-C 202 to retrain to theworst-case profile. Although communication is temporarily halted, sincea new profile need not be calculated, measured or exchanged, the ATU-C202 and the ADSL modem 710 are each able to program their transceiversrelatively quickly and resume communications. Such fast retrainprocedure occurs relatively quickly and may not even be noticed by theuser.

The fast retrain indication transmitted across the transmission medium102 may be performed in any one of several manners. For example, atleast one tone may be used and transmitted by the ADSL modem 710 to theATU-C 202 to provide the fast retrain indication. The ATU-C 202 respondswith the same or a different acknowledge tone. Such a tone-based profileexchange mechanism is particularly reliable and robust to ensure propertransition to the new profile. A constant frequency transmitted in anysub-channel is easily and relatively cheaply detected by both the ADSLmodem 710 and the ATU-C 202.

The predetermined cutback amount must be chosen to ensure thatcommunications resume in the worst possible scenario at the homelocation 702. For example, a disturbance occurs if the handset 705 ofthe phone 704 is lifted off-hook, which would likely cause the ADSLmodem 710 to initiate the fast retrain to the worst-case profile. Thesignal quality degrades even further if a second handset is liftedoff-hook, such as the handset 707 from the phone 706, and degradesfurther still if a third handset is lifted off-hook, such as the handset709 from the phone 708, etc. Since each home location 702 is different,and may include any number of standard phones, a given cutback amountdoes not ensure robust communication in all environments, although areasonable cutback amount may be sufficient for most cases. It iscertain that the predetermined cutback amount causes a significantreduction in performance of ADSL communication via the transmissionmedium 102. Possible cutback amounts are 9, 10, 13, etc. dBm, althoughany arbitrary cutback value is contemplated.

In a second pre-calculated embodiment, a plurality of predeterminedcutback values are used to calculate a corresponding plurality ofcommunication profiles P1, P2, P3, etc. In this case, the ADSL modem 710detects a change or disturbance of the communication on the transmissionmedium 102 and determines which of the plurality of known andprecalculated profiles provides the best performance. The ADSL modem 710uses multiple tones to provide the fast retrain indication according tothe following equation 1:

Log₂ n=x  (1)

where Log is the logarithmic function, base 2, “n” is the number oftotal profiles and “x” is the corresponding number of tones needed toprovide the fast retrain indication. Each combination of tones comprisesa binary index to identify any one of a plurality of differentcommunication profiles. For example, for each tone used for a fastretrain indication, assertion of a tone may represent binary one (1)whereas absence of a tone represents binary zero (0), or vice versa.Four (4) tones are needed to identify any one of up to 16 differentprofiles.

One problem with pre-calculated communication profiles is that few, ifany, of the profiles are optimal for the given communicationcharacteristics. The gain across the frequency band of operation is notlinear, and the effect of each disturbance is also not linear across thesub-channels. Thus, the selected profile represents the worst casesignal quality or SNR drop over all of the sub-channels of the frequencyband. A greater level of performance is possible and attainable byactually measuring the communication parameters of the transmissionmedium 102 in its existing condition. A more efficient set ofpre-calculated profiles may be achieved through more sophisticatedmethods based on experimental results. However, each home location 702has significant variations so that even experimentally determinedpre-calculated profiles would still result in less than optimalcommunication profiles for most locations.

In measurement embodiments, at least one worst-case communicationprofile is measured and stored. In this embodiment, when the ADSL modem710 detects a significant disturbance, such as a handset lifted from aphone, the training logic 810 of the ADSL modem 710 is invoked toperform another full retrain procedure to measure the new communicationcharacteristics of the transmission medium 102 in a similar manner asthe initial procedure described above, and generates a worst-caseprofile. The worst-case profile is then transmitted to the other modemor the ATU-C 202 across the transmission medium 102. The ATU-C 202stores and switches operation to the worst-case profile. Again, only theB&G tables need to be re-generated and the other parameters from theinitial profile remain the same. Since the communication characteristicsof the transmission medium 102 are measured during the disturbance, thenew communication profile enables a more efficient and optimal operationgiven the particular disturbance. However, communications areinterrupted momentarily, such as for several seconds, while the modemperforms the retrain procedure.

The signal quality monitor logic 806 of the ADSL modem 710 continues tomonitor communication on the transmission medium 102 while operatingwith the worst-case profile. If and when the disturbance is removed,such as after a handset is replaced to the on-hook position, the ADSLmodem 710 sends a fast retrain indication to the ATU-C 202 to retrainback to the initial or best-case communication profile. Again, the fastretrain indication may be performed in any one of several manners, suchas one or more predetermined tones. A single tone is sufficient toindicate switching between two communication profiles, therebysimplifying the fast retrain procedure. In this manner, the ADSL modem710 continuously monitors communication on the transmission medium andswitches or retrains between the best and worst-case communicationprofiles depending upon the communication characteristics of thetransmission medium 102 at any given time.

As noted above, a new or different or compounded disturbance may occurso that neither of the measured communication profiles is valid. Forexample, the worst-case profile may have been measured when one of thehandsets, such as the handset 709, was removed from the phone 708. Thehandset 707 may also be removed from the phone 706, causing furtherdepreciation of line and signal quality. In fact, the current worst-casecommunication profile may be invalid so that communication is notpossible or at least compromised. In one measurement and retrainembodiment, the training logic 810 is simply employed to perform anotherretrain procedure to measure and determine a new worst-casecommunication profile that replaces the existing worst-case profile. Thenew worst-case profile is sent to the ATU-C 202, which replaces itscurrent worst-case profile and retrains operation according to the newworst-case profile.

If all the disturbances are removed, the ATU-C 202 and the fast retrainlogic 808 of the ADSL modem 710 perform a fast retrain to switch back tothe best-case profile. If another disturbance occurs, the ADSL modem 710determines if the current worst-case profile is sufficient to enablecommunication to be maintained. If so, the ADSL modem 710 sends a fastretrain indication to the ATU-C 202 and both modems perform a fastretrain to switch to the worst-case profile. It is noted that if thecurrent worst-case profile is sufficient, it is used and anotherworst-case profile is not measured even if the disturbance would allow agreater data rate. In this case, the ATU-C 202 and the memory 812 of theADSL modem 710 store only two communication profiles, including theinitial or best-case profile and a worst-case profile. For example, iffirst, second and third worst-case profiles are consecutively determinedfor one, two and three phones being off-hook, respectively, then onlyone worst-case profile is stored and used, likely associated with threephones being off-hook, even for situations in which only one or twophones are off-hook. This allows a fast retrain to be used for anydisturbance and substantial interruptions are avoided.

In another measurement embodiment, the ATU-C 202 and the ADSL modem 710each store a plurality of measured communication profiles. It ispossible to perform a more sophisticated initialization to measure themost likely disturbances and store corresponding profiles. In a manualinitialization, the user is requested to remove the handsets one at atime and then two at a time, etc., until all desired profiles aredetermined. The manual procedure may be simplified by recognizing thatany single off-hook handset causes approximately the same level ofdisturbance, that any combination of two off-hook handsets also causesapproximately the same level of disturbance, and so on. However, sincesuch disturbances are typically non-linear and based on many complexfactors, a measured profile may not work for all disturbancecombinations. In any event, any such manual initialization is somewhattime-consuming and impractical and would likely not be the most popularsolution.

In a more automated embodiment, each time a disturbance occurs, the fastretrain logic 808 of the ADSL modem 710 determines which of theplurality of stored communication profiles enables communication withthe greatest data rate, if any. If none of the profiles is sufficient,such as, for example, a new disturbance that is greater than anypreviously measured disturbance, then the training logic 810 performs anew measurement procedure to generate a new profile, which is storedwith the other profiles in the memory 812 and sent to the ATU-C 202. Inthis case, however, once a profile is generated, it is stored and is notreplaced by a new worst-case profile. If the initial profile isconsidered a first profile P1, then a second profile P2 is generated forone phone off-hook, a third profile P3 is generated for two phonesoff-hook, a fourth profile P4 is generated for three phones off-hook,and so on.

The system and method of measuring and storing a plurality of profilesuses more memory and requires one of the modems, such as the ADSL modem710, to measure and determine the best profile, if any, to use for eachdisturbance. Nonetheless, each fast retrain is significantly faster thana full retrain and enables more efficient communication since eachdisturbance is effectively measured and evaluated to enable the greatestdata rate available during the existence of that disturbance. It may bedesired to limit the maximum number of possible profiles, such as atotal of sixteen (16) profiles. If 16 profiles are measured and stored,and then an even worse disturbance occurs so that none of the currentprofiles is valid, then the worst of the current 16 is replaced by thenew worst-case communication profile. In most home locations 16 profilesis sufficient for most known and likely disturbances. As statedpreviously, the ADSL modem 710 uses up to 4 tones to rovide a fastretrain indication for up to 16 possible profiles. The ADSL modem 710simply asserts a corresponding combination of the Up to 4 tones torepresent a binary number as an index the appropriate one of the up to16 different profiles.

It is noted that in any of the fast retrain embodiments described above,the ATU-C 202 may also include the same or similar fast retraincapabilities. In that case, if the ATU-C 202 detects a disturbance, itsends a fast retrain request to the ADSL modem 710, which responds withan acknowledge tone and receives a new profile for storage in the memory812. The ADSL modem 710 then retrains the DMT transceiver 804 accordingto the new communication profile to communicate with the ATU-C 202. Ofcourse, the most likely disturbances occur at the home location 702given the more variable environment.

FIG. 9 is flowchart diagram illustrating a fast retrain method accordingto the present invention for a plurality of measured profiles. Themethod shown in FIG. 9 is pcrformed by the ADSL modem 710, the ATU-C202, or both, although operation is illustrated herein with reference tothe ADSL modem 710. In response to detection of at least one DMT signal,operation proceeds to block 901 where the SNR for each DMT tone iscalculated by the signal quality monitor logic 806. Operation proceedsto next block 903 where it is queried whether the SNR is acceptable orgood to maintain communications. If so, operation proceeds to block 905to determine if the modem is in fallback mode. Fallback means that themodem is not operating with the best available communication profile andthat a greater data rate is possible given the current condition of thetransmission medium 102. If the modem is not in fallback, then operationproceeds back to block 901 to repeat the procedure in a continuousmanner. In this manner, the signal quality monitor logic 806continuously monitors the DMT tones received by the DMT transceiver 804.

If the SNR is not acceptable as determined at block 903, or if the modemis operating in fallback as determined at block 905, then operationproceeds to block 907 where the fast retrain logic 808 selects a knownprofile from the memory 812 that is suitable for the measured signalquality. At this point, the signal quality has either improved and abetter profile is available for more efficient operation or the signalquality has depreciated and another profile is needed to maintaincommunications. Operation proceeds to next block 909 to determine if acommunication profile is available in the memory 812 that is suitablefor the measured signal quality. If a suitable profile is found in thememory 812, operation proceeds to next block 911 where the fast retrainlogic 808 initiates a profile change procedure. The fast retrainindication is sent to a remote modem, such as the ATUC-202, and theretrain procedure is acknowledged. Operation then proceeds to next block913 where the fast retrain logic 808 changes to the newly selectedprofile and then to block 915 where the DMT transceiver 804 is retrainedaccording to the newly selected profile. Operation then returns to block901 for continuous signal quality monitoring.

If a suitable profile is not available in the memory 812 as determinedat block 909, then operation proceeds instead to block 917, where theinitialization and training logic 810 initiates a full retrainprocedure. At this point, the remote modem, such as the ATU-C 202, iscapable of detecting that a full retrain procedure is occurring.Operation proceeds to next block 919 where the training logic 810generates and stores a new profile in the memory 812. Operation thenproceeds to block 915, where the DMT transceiver 804 is retrainedaccording to the newly measured and stored profile, and then operationreturns to block 901 for continuous signal quality monitoring.

It is now appreciated that a digital modem and modem system thatsupports fast retrain based on communication profiles according to thepresent invention enables efficient ADSL communications for a homelocation without a POTS splitter. Disturbances in the line or signalquality are detected and measured and a new profile is generated andexchanged between the modems. Both modems adapt to the new communicationcharacteristics by retraining according to the new communicationprofile. At least two profiles, including a best-case profile and aworst-case profile, enable communications to continue with little or nointerruption. When operating according to one of two profiles, if one ofthe modems detects a disturbance or removal of a disturbance, it sends afast retrain indication and both modems switch to operate according tothe other profile. A plurality of profiles may also be generated andused, where one modem determines the proper profile and asserts the fastretrain indication to identify the appropriate profile. In this manner,both modems quickly retrain according to the same profile and resumecommunications.

Although the system and method of the present invention has beendescribed in connection with the preferred embodiment, it is notintended to be limited to the specific form set forth herein, but on thecontrary, it is intended to cover such alternatives, modifications, andequivalents, as can be reasonably included within the spirit and scopeof the invention as defined by the appended claims.

What is claimed is:
 1. A digital modem for coupling to a transmissionmedium, comprising: a memory that stores a plurality of communicationprofiles; communication logic that sends and receives information viathe transmission medium and that operates according to any one of theplurality of communication profiles; monitor logic that continuouslymonitors communication by the communication logic on the transmissionmedium according to any one of the plurality of communication profilesand that provides a signal change indication if the communicationcharacteristics change by at least a predetermined amount; and fastretrain logic that selects another one of the plurality of communicationprofiles stored in the memory in response to the signal changeindication, that retrains the communication logic to operate accordingto the selected communication profile and that cooperates with thecommunication logic to transmit a fast retrain indication via thetransmission medium.
 2. The digital modem of claim 1, furthercomprising: measuring logic that cooperates with the communication logicto measure the communication characteristics of the transmission mediumand that generates and stores a corresponding communication profile intothe memory; and each of the plurality of communication profiles beingmeasured and stored by the measuring logic in cooperation with thecommunication logic.
 3. The digital modern of claim 2, furthercomprising: the fast retrain logic receiving the signal changeindication and determining that none of the plurality of communicationprofiles is valid based on the communication characteristics andproviding a new profile indication; the measuring logic receiving thenew profile indication, cooperating with the communication logic tomeasure the communication characteristics of the transmission medium andgenerating and storing a corresponding new communication profile intothe memory; and the measuring logic cooperating with the communicationlogic to send the new communication profile via the transmission medium.4. The digital modem of claim 1, wherein the fast retrain indication istone based.
 5. The digital modem of claim 4, further comprising: thefast retrain indication comprising a plurality of tones that provides anindex to the plurality of communication profiles.
 6. A digital modemsystem, comprising: a transmission medium; a first modem, coupled to thetransmission medium, comprising: a first memory that stores a pluralityof communication profiles; communication logic that sends and receivesinformation via the transmission medium and that operates according toany one of the plurality of communication profiles; monitor logic thatcontinuously monitors communication by the communication logic on thetransmission medium according to any one of the plurality ofcommunication profiles and that provides a signal change indication ifthe communication characteristics change by at least a predeterminedamount; and first fast retrain logic that selects another one of theplurality of communication profiles stored in the memory in response tothe signal change indication, that retrains the communication logic tooperate according to the selected communication profile and thatcooperates with the communication logic to transmit a fast retrainindication via the transmission medium; and a second modem, coupled tothe transmission medium, comprising: a second memory that stores theplurality of profiles; second communication logic that receives andoperates according to any communication profile sent by the first modem;and second fast retrain logic that, upon detecting the fast retrainindication sent by the first modem, retrains the second communicationlogic to operate according to the selected communication profile.
 7. Thedigital modem system of claim 6, further comprising: the first memoryand the second memory storing at least a first and a secondcommunication profile; the first and second communication logicoperating according to the second communication profile; the monitorlogic detecting the communication characteristics improve by at leastthe predetermined amount and providing the signal change indication; thefirst fast retrain logic retraining the first communication logic tooperate according to the first communication profile and cooperatingwith the first communication logic to transmit a fast retrain indicationvia the transmission medium to the second modem; and the second modemreceiving the fast retrain indication and the second fast retrain logicretraining the second communication logic to operate according to thefirst communication profile.
 8. The digital modem system of claim 7,further comprising: the monitor logic detecting the communicationcharacteristics depreciate by at least the predetermined amount andproviding the signal change indication; the first fast retrain logicretraining the first communication logic to operate according to thesecond communication profile and cooperating with the communicationlogic to transmit a fast retrain indication via the transmission medium;and the second modem receiving the fast retrain indication and thesecond fast retrain logic retraining the second communication logic tooperate according to the second communication profile.
 9. The digitalmodem of claim 7, further comprising: the monitor logic detecting thecommunication characteristics depreciate by at least the predeterminedamount and providing the signal change indication; the first fastretrain logic determining that that first and second communicationprofiles are not suitable and providing a new profile indication;measurement logic, in response to the new profile indication, thatcooperates with the first communication logic to measure thecommunication characteristics of the transmission medium and thatgenerates and stores a corresponding third communication profile intothe memory; the measurement logic training the first communication logicto operate according to the third communication profile and cooperatingwith the first communication logic to transmit the third communicationprofile via the transmission medium; and the second modem receiving andstoring the third communication profile into the second memory andretraining the second communication logic to operate according to thethird communication profile.
 10. The digital modem of claim 9, whereinthe third communication profile replaces the second communicationprofile and wherein the fast retrain indication comprises a single tone.11. The digital modem of claim 9, wherein the first memory stores thefirst, second and third communication profiles and wherein the fastretrain indication comprises a plurality of tones to provide a binaryindex to the plurality of communication profiles.
 12. The digital modemof claim 6, further comprising: the first modem including measuringlogic that cooperates with the first communication logic to measure thecommunication characteristics of the transmission medium uponinitialization and that generates and stores a corresponding firstcommunication profile into the first memory; the measurement logiccooperating with the first communication logic to send the firstcommunication profile to the second modem via the transmission medium;the measurement logic calculating at least one more communicationprofile based on the first communication profile and a predeterminedcutback amount and storing the at least one more communication profilein the first memory; the second modem receiving and storing the firstcommunication profile; and the second modem independently calculatingthe at least one more communication profile based on the firstcommunication profile and the predetermined cutback amount and storingthe at least one more communication profile in the second memory.